1. Field of the Invention
This invention relates to radar systems and more particularly, to the elimination or reduction of the effect of jamming in a frequency scan radar system.
2. Description of the Prior Art
In the prior art, various systems have been proposed whereby the inherent frequency sensitivity of certain antenna configurations is employed in conjunction with variable frequency transmitter to effect inertialess scanning. The variable frequency transmitting and receiving characteristic of such systems makes them inherently less susceptible to jamming of the classic type. This is true, not only because of the variable frequency feature, but also because such systems frequently employ pencil-beams which "see" a jammer source much less frequently in their scanning schedule than is the case for fan beam systems such as the prior art conventional Plan Position Indicator radar which radiates a beam wide in the elevation plane to provide unrestricted elevation coverage and narrow in the azimuth plane to provide resolution of targets for the PPI presentation.
Nevertheless, more sophisticated jamming techniques can be employed which tend to limit the usefulness of even the pencil-beam frequency scan radar system in a hostile environment.
A prior art system in respect to the present invention is described in co-pending United States application Ser. No. 599,348 filed Dec. 2, 1966, and assigned to the same assignee as the present invention. In that reference, a system is described which provides a PPI presentation and also a range-height presentation by scanning a pencil-beam in the vertical plane (for example, from the horizon to plus 45.degree.) at a rapid rate while the entire antenna system is being rotated in the azimuth plane throughout an angle such as 360.degree.. The present invention is a system improvement, particularly adaptable to the aforementioned frequency-scan system.
Another prior art frequency scan radar system to which the present invention is generally applicable is described in U.S. Pat. No. 3,039,097.